Tiny Five-Stroke Engine Promises Big Fuel Economy

Tiny Five-Stroke Engine Promises Big Fuel Economy
By Keith Barry August 21, 2009 | 6:30 am | Categories: Performance

The four-stroke engine has dominated internal combustion for more than a century, but a British engineering firm is ready to topple that technology with what it calls a 150-horsepower “five-stroke” engine said to offer the fuel economy of a diesel without the particulate emissions.

Ilmor Engineering, a firm that is co-owned by Roger Penske and supplies Honda engines to the Indy Racing League, spent almost 20 years developing the three-cylinder engine. Two cylinders operate on the conventional four-stroke cycle and empty their exhaust into a third low-pressure expansion cylinder, which allows the expansion and compression processes to operate independently. The prototype engine was first displayed at the 2009 Stuttgart Engine Expo, and its being readied for real-world, under-the-hood testing.

The Otto cycle four-stroke engine has pretty much been the standard for 132 years, but the five-stroke engine might be a great stopgap between current technology and the Next Big Thing.

According to Ilmor, the 0.7-liter engine is capable of 150 brake horsepower and weighs 20 percent less than engines with a similar output. Brake specific fuel consumption of the prototype is 226 g/kWh, which is a 10 percent improvement over current four-stroke technology. Even better, Ilmor says the technology is “100% conventional” and doesn’t require any new manufacturing techniques.

Ilmor says that the prototype five-stroke engine, based on a design by Gerhard Schmitz, has an overall expansion ratio “approaching that of a diesel engine – in the region of 14.5:1.” Along with its light weight and relatively high output, the extra work done in the low pressure (LP) cylinder provides for better fuel economy.

“Running of the concept engine has produced impressive fuel consumption readings over a very wide operating range,” the company said in a statement. “This is because at the onset of knock a greater percentage of work can be extracted in the LP cylinder, giving a degree of self compensation.”

Ilmor says the prototype is ready for road testing and could be used as a conventional engine or as part of a hybrid drivetrain. The company says it is “keen” to find a partner to help develop the engine and it is talking to automakers and top suppliers about the technology.

Photo of the “five-stroke” engine: Ilmor Engineering.

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Posted by: richardgeller | 08/21/09 | 7:40 am
Everyday it seems we hear news about new and promising approaches to cleaner-burning, more fuel-efficient technologies. I guess the old saying is true, “where there’s a will there’s a way,” or maybe “necessity is the mother of invention.”
Richard Geller
http://www.aSiteAboutSomething.com

Posted by: Tom_B | 08/21/09 | 10:04 am
I read this and noticed 150 BHP from 0.7 liter was characterised as “relatively high output”. I thought this was amazing output from a commercial engine so I checked the facts on Ilmor’s website. It is really 150 BHP / liter. Thus a 0.5 liter engine should have 105 BHP which is much more believable although still high. My 1.8 Versa can only manage 122 BHP. An Ilmor 1.8 should give me 270 BHP. Yes!!

Posted by: Delta5 | 08/21/09 | 11:24 am
Tom_B, exactly what I was thinking.

Low emissions and high efficiency are great things. Kudos for that. But 150bhp from a .7 liter engine? THAT, is extraordinary. 100hp/L is often the benchmark for a ‘great’ engine design, and forced-induction (turbo,supercharged) engines in high-performance street cars can approach 150hp/L (2.0L Mitsubishi EVO’s making ~300hp). But to get 150BHP from .7L, they’re at more than *200hp*/L, and I didn’t see anything about being a forced-induction engine, so holy cow. That’s extraordinary!!

If this design proves to be durable and can be manufactured at a market-acceptable cost, then this design could be truly revolutionary. Simply from a power-weight-efficiency standpoint.

Posted by: phrancis | 08/21/09 | 12:17 pm
@Delta5, yeah that would be great if all the claims are true and can be made cheap and reliable. Since the compression is already high, could you even turbo that thing? That would be even more amazing. Didn’t Volvo have a 5 stroke? or maybe I’m thinking 5 cylinder…

Posted by: Gifftor | 08/21/09 | 1:11 pm
@phrancis - I think you’re thinking 5-cylinder; Hummer put one in its H3, as well (no, I’m not a Hummer fan, I just remember reading that it was underpowered).

Posted by: JimBullis | 08/21/09 | 3:42 pm
Sounds great but oops, the Prius engine already does this well. It gets 38% efficiency just by valve timing changes and, I think mostly, using it in limited load and speed variations.

Posted by: stevew | 08/22/09 | 12:11 am
re: Horsepower per liter. Recent engine: Honda’s S2000 made 120 bhp/liter. Historical (monster) engine: BMW’s 1986 Formula 1 turbo motors 876 bhp/liter (1300 bhp from 1499cc). http://www.gurneyflap.com/bmwturbof1engine.html

Posted by: toby34a | 08/24/09 | 5:42 pm
This will be nice to see in a Penske Saturn in a few years